Billowing phenomenon refers to the presence of contrast medium on contrast-enhanced CT outside of graft metal struts, due to the specific construction characteristic typical of the AFX® stent-graft (Endologix, Inc., USA), designed to treat abdominal aortic aneurysms. It has a unique internal scaffolding design in which ePTFE material is attached only to the most proximal and distal stent tips. The ePTFE material is not attached to the stent cage over its entire length and can move independently of the metal struts. This outward movement is referred to as billowing, which is supposed to accommodate aortic aneurysm tortuosity or wall irregularity. Billowing phenomenon can mimic and be misdiagnosed as a type I or type III endoleak.
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